linux-kernel - [PATCH] thermal: rcar_gen3_thermal: Fix Wshift-negative-value

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Date:   Thu, 13 Jun 2019 14:12:28 -0700
From:   Nathan Huckleberry <nhuck@...gle.com>
To:     rui.zhang@...el.com, edubezval@...il.com, daniel.lezcano@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Huckleberry <nhuck@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: [PATCH] thermal: rcar_gen3_thermal: Fix Wshift-negative-value

Clang produces the following warning

vers/thermal/rcar_gen3_thermal.c:147:33: warning: shifting a negative
signed value is undefined [-Wshift-negative-value] / (ptat[0] - ptat[2])) +
FIXPT_INT(TJ_3); ^~~~~~~~~~~~~~~ drivers/thermal/rcar_gen3_thermal.c:126:29
note: expanded from macro 'FIXPT_INT' #define FIXPT_INT(_x) ((_x) <<
FIXPT_SHIFT) ~~~~ ^ drivers/thermal/rcar_gen3_thermal.c:150:18: warning:
shifting a negative signed value is undefined [-Wshift-negative-value]
tsc->tj_t - FIXPT_INT(TJ_3)); ~~~~~~~~~~~~^~~~~~~~~~~~~~~~

Upon further investigating it looks like there is no real reason for
TJ_3 to be -41. Usages subtract -41, code would be cleaner to just add.

Fixes: 4eb39f79ef44 ("thermal: rcar_gen3_thermal: Update value of Tj_1")
Cc: clang-built-linux@...glegroups.com
Link: https://github.com/ClangBuiltLinux/linux/issues/531
Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
---
 drivers/thermal/rcar_gen3_thermal.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/thermal/rcar_gen3_thermal.c b/drivers/thermal/rcar_gen3_thermal.c
index a56463308694..f4b4558c08e9 100644
--- a/drivers/thermal/rcar_gen3_thermal.c
+++ b/drivers/thermal/rcar_gen3_thermal.c
@@ -131,7 +131,7 @@ static inline void rcar_gen3_thermal_write(struct rcar_gen3_thermal_tsc *tsc,
 #define RCAR3_THERMAL_GRAN 500 /* mili Celsius */
 
 /* no idea where these constants come from */
-#define TJ_3 -41
+#define TJ_3 41
 
 static void rcar_gen3_thermal_calc_coefs(struct rcar_gen3_thermal_tsc *tsc,
 					 int *ptat, const int *thcode,
@@ -144,11 +144,11 @@ static void rcar_gen3_thermal_calc_coefs(struct rcar_gen3_thermal_tsc *tsc,
 	 * the dividend (4095 * 4095 << 14 > INT_MAX) so keep it unscaled
 	 */
 	tsc->tj_t = (FIXPT_INT((ptat[1] - ptat[2]) * 157)
-		     / (ptat[0] - ptat[2])) + FIXPT_INT(TJ_3);
+		     / (ptat[0] - ptat[2])) - FIXPT_INT(TJ_3);
 
 	tsc->coef.a1 = FIXPT_DIV(FIXPT_INT(thcode[1] - thcode[2]),
-				 tsc->tj_t - FIXPT_INT(TJ_3));
-	tsc->coef.b1 = FIXPT_INT(thcode[2]) - tsc->coef.a1 * TJ_3;
+				 tsc->tj_t + FIXPT_INT(TJ_3));
+	tsc->coef.b1 = FIXPT_INT(thcode[2]) + tsc->coef.a1 * TJ_3;
 
 	tsc->coef.a2 = FIXPT_DIV(FIXPT_INT(thcode[1] - thcode[0]),
 				 tsc->tj_t - FIXPT_INT(ths_tj_1));
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog